Optimization of HashTraits<RefPtr<P> >::emptyValue()

HashTraits<RefPtr<P> >::emptyValue() is better just to return zero pointer
rather than access static RefPtr instance, further HashTraits<RefPtr<P> >::passOut() can be overriden to accept raw pointer (for empty value).
This all should improve HashMap performance in case its value type is RefPtr.

Review URL: https://chromiumcodereview.appspot.com/14877006

git-svn-id: svn://svn.chromium.org/blink/trunk@150425 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed